System and method for treatment of a flue gas

ABSTRACT

A method for treatment of a flue gas involves feeding the flue gas and a lean solvent to an absorber. The method further involves reacting the flue gas with the lean solvent within the absorber to generate a clean flue gas and a rich solvent. The method also involves feeding the clean flue gas from the absorber and water from a source, to a wash tower to separate a stripped portion of the lean solvent from the clean flue gas to generate a washed clean flue gas and a mixture of the water and the stripped portion of the lean solvent. The method further involves treating at least a portion of the mixture of the water and the stripped portion of the lean solvent via a separation system to separate the water from the stripped portion of the lean solvent.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH & DEVELOPMENT

This invention was made with Government support under contract numberDE-FE0013755 awarded by the Department of Energy (DOE). The Governmenthas certain rights in this invention.

BACKGROUND

The invention relates generally to gas treatment systems, and moreparticularly to a system and a method for treatment of a post combustionflue gas.

In combustion-based systems such as a power plant, for example, a fluegas is produced when coal or other types of fuel are burned in air. Theheat released by combustion generates steam, which drives a turbinegenerator for producing electric power. Hot combustion gases exiting theboiler include nitrogen and smaller concentrations of water vapor andcarbon dioxide. Other constituents, formed from impurities in coal,include sulfur dioxide, nitrogen oxides, and particulate matter (flyash). Such pollutants must be removed to meet environmental standards.

One effective method to remove carbon dioxide from the flue gas is bychemical reaction with a liquid solvent because the flue gas is atatmospheric pressure and the concentration of carbon dioxide is low(typically around 12-15% by volume for coal plants, for example). Themost commonly used solvents are a family of organic amines, a subclassfor example, are amino silicones. The flue gas is “scrubbed” with anamine solution, inside a vessel referred to as an absorber, typicallycapturing a higher percentage of the carbon dioxide. The carbondioxide-laden solvent is then pumped to another vessel, referred to as aregenerator, where heat releases the carbon dioxide as a gas. Theresulting concentrated carbon dioxide gas stream is then compressed intoa supercritical fluid for transport and the solvent is recycled.

Amino silicone, for example, is an expensive solvent. The drawbacksassociated with conventional treatment systems are that there is asubstantial loss of the amino silicone solvent along with the clean fluegas exiting the absorber.

There is a need for an enhanced system and method for treatment of fluegas to reduce a solvent loss.

BRIEF DESCRIPTION

In accordance with one exemplary embodiment, a method for treatment of aflue gas is disclosed. The method involves feeding the flue gas and alean solvent to an absorber. The method further involves reacting theflue gas with the lean solvent within the absorber to generate a cleanflue gas and a rich solvent. The method also involves feeding the cleanflue gas from the absorber and water from a source, to a wash tower toseparate a stripped portion of the lean solvent from the clean flue gasto generate a washed clean flue gas and a mixture of the water and thestripped portion of the lean solvent. The method further involvestreating at least a portion of the mixture of the water and the strippedportion of the lean solvent via a separation system to separate thewater from the stripped portion of the lean solvent.

In accordance with another exemplary embodiment, a system for treatmentof a flue gas is disclosed. The system includes an absorber forreceiving a flue gas and configured to react the flue gas with a leansolvent to generate a clean flue gas and a rich solvent. The systemfurther includes a wash tower coupled to the absorber and a source, forreceiving the clean flue gas and water respectively and configured toseparate a stripped portion of the lean solvent from the clean flue gasto generate a washed clean flue gas and a mixture of the water and thestripped portion of the lean solvent. The system further includes aseparation system coupled to the wash tower and configured to treat atleast a portion of the mixture of the water and the stripped portion ofthe lean solvent to separate the water from the stripped portion of thelean solvent.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic block diagram illustrating a system for treatmentof a flue gas in accordance with an exemplary embodiment; and

FIG. 2 is a schematic block diagram illustrating an absorber coupled toa separation system in accordance with an exemplary embodiment.

DETAILED DESCRIPTION

In accordance with certain embodiments of the present invention, amethod for treatment of a flue gas is disclosed. The method furtherinvolves feeding a flue gas and a lean solvent to an absorber andreacting the flue gas with the lean solvent within the absorber togenerate a clean flue gas and a rich solvent. The method also involvesfeeding the clean flue gas from the absorber and water from a source, toa wash tower to separate a stripped portion of the lean solvent from theclean flue gas to generate a washed clean flue gas and a mixture of thewater and the stripped portion of the lean solvent. The method furtherinvolves treating at least a portion of the mixture of the water and thestripped portion of the lean solvent via a separation system to separatethe water from the stripped portion of the lean solvent. In accordancewith certain other embodiments, a system for treatment of a flue gas isdisclosed. The lean solvent is removed from the cleaned flue gas andrecirculated back for further use in the treatment of the flue gas.

Referring to FIG. 1, a schematic block diagram illustrating a system 10for treatment of a flue gas 12 in accordance with an exemplaryembodiment is illustrated. The system 10 includes a cooler 14, forexample, a direct contact cooler, coupled to an absorber 18. Theabsorber 18 is coupled via a pump 20 to a heat exchanger 22. The heatexchanger 22 is also coupled via a cooler 24 to the absorber 18. Theheat exchanger 22 is further coupled to a desorber 26.

The system 10 further includes a solvent loop 28 having a pump 30 and aheater 32 coupled to the desorber 26. The desorber 26 and the solventloop 28 together form a treatment device 29. The desorber 26 is furthercoupled to a separator 34 via a cooler 36. The separator 34 is coupledto a compressor 38, for example, a multi-stage compressor. The cooler 14and the compressor 38 are coupled to a separation system 40. Theseparation system 40 is explained in greater with reference tosubsequent figures.

During operation of the system 10, the flue gas 12 from a source such asa combustor, for example, is fed via the cooler 14 to cool the flue gas12 to form a mixture of cooled flue gas 42 and water 44. The cooler 14further separates the flue gas 42 from the water 44. The flue gas 42 anda lean solvent 46 are fed to the absorber 18. The flue gas 42 and thelean solvent 46 react (i.e. reversible chemical reaction) within theabsorber 18 to generate a clean flue gas 48 and a rich solvent 50.

In one embodiment, the lean solvent 46 includes a mixture ofaminosilicone and triethylene glycol. In one specific embodiment, theamino silicone is an amino propyl terminated dimethylsiloxane, wherein X(as described herein) may be from 0 to 10 or a mixture. Theaminosilicones are generally referred to as GAP-X, where X is equal tothe number of dimethyl siloxy repeat units. An absorbing medium from theGAP-X medium may include hindered amines such as methyldiethanolamine(“MDEA”), 2-amino-2-methyl-1-propanol (“AMP”). Optionally, the absorbingmedium may also include other components, such as, for example,oxidation inhibitors, corrosion inhibitors and anti-foaming agents.

The lean solvent 46 absorbs the carbon dioxide from the flue gas 42 togenerate the clean flue gas 48. The term “clean flue gas” may bereferred to as a flue gas with reduced level of carbon dioxide. The term“lean solvent” may be referred to as a solvent with a substantiallyreduced level of carbon dioxide. The term “rich solvent” may be referredto as a solvent having an increased level of carbon dioxide.Specifically, the “rich solvent” may be referred to as a solvent havingan increased level of carbon dioxide relative to the “lean solvent” as aresult of absorbing the carbon dioxide from the flue gas 42. A minimalconcentration difference between the rich solvent and the lean solventmay be about 1% by weight. An example of an amino silicone isrepresented by:

The rich solvent 50 is fed from the absorber 18 to the heat exchanger 22via the pump 20. The rich solvent 50 is fed in heat exchangerelationship with the lean solvent 46 via the heat exchanger 22. Thelean solvent 46 is fed from the heat exchanger 22 via the cooler 24 tothe absorber 18. The rich solvent 50 is then fed to the desorber 26. Aportion of the rich solvent 50 is re-circulated via the solvent loop 28having the pump 30 and the heater 32 to heat the portion of the richsolvent 50 and feed to the desorber 26. As a result, carbon dioxide 52is desorbed from the rich solvent 50 to generate the lean solvent 46.The lean solvent 46 is fed via the heat exchanger 22 and the cooler 24to the absorber 18.

Carbon dioxide 52 is cooled via the cooler 36 and then fed to theseparator 34. The separator 34 separates a condensate 54 from the carbondioxide 52. The condensate 54 is fed back to the desorber 26 and thecarbon dioxide 52 is compressed within the compressor 38. A compressedcarbon dioxide 56 is exhausted from the compressor 38.

The clean flue gas 48 and water from a source are fed to the separationsystem 40. In the illustrated embodiment, the source is the cooler 14.The water 44 is fed from the cooler 14 to the separation system 40. Inanother embodiment, the source is the compressor 38 and cooling waterfrom the compressor 38 is fed to the separation system 40. In certainother embodiments, water from other sources may also be fed to theseparation system 40. For example, the water may be pure water or maypotentially include solvents/chemicals.

In conventional configurations, a large amount of a solvent may be lostalong with a clean flue gas stream. In accordance with the embodimentsdiscussed herein, the separation system 40 is used to separate astripped portion of the lean solvent 46 from the clean flue gas 48 andrecirculate it back to the system 10. It should be noted herein that thestripped portion of the lean solvent 46 is referred to as a removedportion of the lean solvent 46 either in the form of vapor or aerosol.

Referring to FIG. 2, a schematic block diagram illustrating the absorber18 coupled to the separation system 40 in accordance with an exemplaryembodiment is illustrated. The absorber 18 and the compressor 38 (shownin FIG. 1) are coupled to a wash tower 58. The wash tower 58 is furthercoupled to a decanter 60 via a flow splitter 62. The decanter 60 iscoupled via a membrane separator 64 to a distillation device 66.Further, the decanter 60 is directly coupled to the distillation device66 via a bypass valve 67 and a bypass path 69. In another embodiment,the membrane separator 64 and the distillation device 66 may not beused.

As discussed previously, during operation the clean flue gas 48 andwater from a source are fed to the separation system 40. In theillustrated embodiment, the source is the cooler 14 (shown in FIG. 1).Specifically, the water 44 from the cooler 14 and the clean flue gas 48are fed to the wash tower 58. The clean flue gas 48 is cooled via thecooler 59 before being fed to the wash tower 58. In another embodiment,the source is the compressor and cooling water from the compressor 38 isfed to the separation system 40. In certain other embodiments, waterfrom other sources may also be fed to the separation system 40.

In the illustrated embodiment, a stripped portion 68 of the lean solventis separated from the clean flue gas 48 within the wash tower 58, usingthe water 44, to generate a washed clean flue gas 70 and a mixture 72 ofthe water 44 and the stripped portion 68 of the lean solvent. The term“washed clean flue gas” may be referred to as a flue gas without thestripped portion of the lean solvent. Further, separating at least aportion 74 of the mixture 72 of the water 44 and the stripped portion 68of the lean solvent is split via the splitter 62 and fed to the decanter60. A remaining portion 76 of the mixture 72 of the water 44 and thestripped portion 68 of the lean solvent is recirculated back to the washtower 58. In one embodiment, a portion 74 of the mixture 72 of the water44 and the stripped portion 68 of the lean solvent includes 95% byweight of water and 5% by weight of the stripped portion 68 of the leansolvent. In other embodiments, the percentage by weight of the water 44and the stripped portion 68 of the lean solvent may vary depending uponthe application.

Further, in the illustrated embodiment, a water phase portion 78 isseparated from a solvent phase portion 80 of at least the portion 74 ofthe mixture 72 of the water 44 and the stripped portion 68 of the leansolvent via the decanter 60, under the influence of gravity because ofimmiscibility of the water phase portion 78 and the solvent phaseportion 80. In one embodiment, the water phase portion 78 includes about1%-3% of the stripped portion of the lean solvent; and the solvent phaseportion 80 includes about 30% water and 70% of the stripped portion ofthe lean solvent. In other embodiments, the percentage by weight of thewater and the stripped portion of the lean solvent may vary dependingupon the application.

Further, in the illustrated embodiment, a first portion 82 of the water44 is separated from the water phase portion 78 via the membraneseparator 64 to generate a first solvent portion 84. In one embodiment,the first solvent portion 84 includes 60% by weight of water and 40% byweight of the stripped portion of the lean solvent. In otherembodiments, the percentage by weight of the water and the strippedportion of the lean solvent may vary depending upon the application.

A second portion 86 of the water 44 is then separated from the firstsolvent portion 84 via the distillation device 66 to generate a secondsolvent portion 88. The second solvent portion 88 is then recirculatedback to the absorber 18. In another instance, if the water phase portion78 is fed from the decanter 60 to the distillation device 66 via thebypass path 69, a portion of the water is separated from the water phaseportion 78 via the distillation device 66 to generate a solvent portion.

In accordance with the embodiments of the present invention, the cleanflue gas 48 is contacted with the water stream 44 in the wash tower 58.The water 44 cools the clean flue gas 48 and therefore reduces the vaporpressure of the stripped lean solvent in the clean flue gas 48. Hence, asubstantial percentage of the stripped lean solvent is removed by thewater 44, resulting in enhanced separation of the stripped lean solventvia the decanter 60 and the membrane separator 64

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

The invention claimed is:
 1. A system for treatment of a flue gas, thesystem comprising: an absorber for receiving a flue gas and configuredto react the flue gas with a lean solvent to generate a clean flue gasand a rich solvent; a wash tower coupled to the absorber and a source,for receiving the clean flue gas and water respectively and configuredto separate a stripped portion of the lean solvent from the clean fluegas to generate a washed clean flue gas and a mixture of the water andthe stripped portion of the lean solvent; and a separation systemcomprising a splitter coupled to the wash tower and a decanter coupledto the splitter, wherein the splitter is configured to separate at leasta portion of the mixture of the water and the stripped portion of thelean solvent, and wherein the decanter is configured to separate a waterphase portion from a solvent phase portion of at least the portion ofthe mixture of the water and the stripped portion of the lean solvent.2. The system of claim 1, wherein the lean solvent comprisesaminosilicone.
 3. The system of claim 1, wherein the absorber is furtherconfigured to remove carbon dioxide from the flue gas, using the leansolvent.
 4. The system of claim 1, wherein the separation system furthercomprises a distillation device coupled to the decanter via a bypasspath and configured to separate at least a portion of the water from thewater phase portion to generate a solvent portion.
 5. The system ofclaim 1, further comprising a treatment device coupled to the absorberand configured to receive the rich solvent and treat the rich solvent toseparate carbon dioxide from the rich solvent.
 6. The system of claim 1,wherein the separation system further comprises a membrane separatorcoupled to the decanter and configured to separate at least a firstportion of the water from the water phase portion to generate a firstsolvent portion.
 7. The system of claim 6, wherein the separation systemfurther comprises a distillation device coupled to the membraneseparator and configured to separate a second portion of the water fromthe first solvent portion to generate a second solvent portion.
 8. Thesystem of claim 7, wherein the system is configured to recirculate thesecond solvent portion to the absorber.